The invention deals with a submersible drive unit with pressure medium pumps connected with a pressure medium tank and driven by underwater electric motors, connectable with the drive of submersible pile drivers and work units.
For underwater pile driving on the sea floor, the pressure medium required for driving the equipment is supplied through a pressure medium circuit with long hoses from above the water surface to the work unit. Because of the flow resistance in the hoses, this is only feasible up to a water depth where the pressure medium pumps can still cope with the additional pressure required to overcome this resistance. Finally, the limits of feasibility, economy and also handling are reached.
In this case a submersible drive unit is connected with the equipment and lowered together with it, supplying a pressure medium through a short circuit, while, for the operation of the drive unit, electric energy is supplied through a long electric power cable from above the water surface with now much lower resistance, i.e. energy losses.
DE-PS 24 54 521 discloses a drive unit, consisting of pressure medium pumps, each driven by an electric motor, and a tank containing the pressure medium, and is displaceable in upward and downward directions by shock absorbing means, and is guided on the pressure medium cylinder of a rammer projecting from the upper end of the housing of a ramming device, and is connected with the latter through short and flexible lines.
This known drive unit requires a precise form fit to the upper end of the ramming device, a shock absorbing displaceable guide at the ramming device, and an attachment to the latter through shock absorbing means, by means of bolts or similar fasteners.
The underwater drive unit currently in use shows especially the following disadvantages:
the manufacture of machined surfaces on the relatively large parts required for a displaceable guide is expensive, and these surfaces are difficult to repair when damaged, PA1 the structure for guiding and supporting all components is heavy and relatively expensive, PA1 the firm connection with the ramming device can only be disconnected on the deck of the support ship, which requires correspondingly long repair and/or change-over times, PA1 the design is not conducive to the replacement of individual components, PA1 there is no quick access to the drive unit of the ramming device in case of damage.
Further, EP-PS 03 01 116 discloses an underwater drive unit comprising electric motors, pumps and pressure medium tank, which is connected with the drive of a pile driver or work unit by means of flexible conduits.
This drive unit has a cover housing with a concentric shaft which goes all the way through to accommodate a foundation pile or the necessary installation equipment, lower and upper support plates which are connected with the outer wall whose internal surface and the inner wall enclosing the shaft form an annulus in which electric motor/pump units are arranged parallel to the shaft. These electric motor/pump units are restrained by springs to limit and cushion movements relative to the cover housing and parallel to the shaft.
This design has disadvantages also. Considerable work time on the deck of the support ship is required in order to separate the drive unit from the work unit and to remove it from the shaft. Moreover, the cover housing, serving both as a guide and as a structure for attaching drive unit components is heavy and expensive, because of the inner and outer walls and the upper and lower support plates.
Apart from the need to eliminate these disadvantages, there are difficulties regarding economy and safety due to the overall configuration and working conditions of pile drivers and work units. They pertain to handling methods, outfitting expenditure, better utilization of the drive unit and its individual components.
As to handling, difficulties occur frequently with the umbilical which connects the support ship with the drive unit/work unit. This umbilical contains electric power cables for the transmission of drive energy to the underwater electric motors of the drive unit and at least one line for the supply of compressed air to the work unit to compensate for the outer pressure on enclosed hollow spaces, and control lines for controlling and monitoring the drive unit and work unit. All these lines are contained in one conduit only, the umbilical, so that one need only handle one line.
The umbilical is equipped with a strong outer armor to protect the internal lines and to bear lifting loads. It can cost up to US $1400.00 per meter. Fear of damage discourages its use.
The above mentioned difficulties arise, because the pile driver or work unit is rigidly attached to the drive unit to which the umbilical is rigidly attached, and because these parts must always be handled together and moved in unison when picked up on deck, during lowering to the pile deep underwater, and when laid down on deck. Because of rough handling the umbilical can hook on, twist around and catch on any object on deck, on the underwater structure or on the drive unit or on the work unit itself. The result of these difficulties is damage.
The costs for the heavy umbilical with hoist and pile driver/drive unit are further increased because, for fear of failure of lines inside the umbilical and/or motor/pump units, additional electric power cables and control lines are included in the umbilical and the drive unit is equipped with additional or bigger motor/pump units than required. This is done because, when such a failure occurs, quick repairs are currently not possible and the cost for one hour downtime of a support ship can be up to US $17,000.00.
In addition, the operating speed of the work unit is partly measured by standards based on well established pile driving work above water, resulting in costs which, for underwater work, are not commensurate with the derived benefits. The deeper the operation, the more time is required for handling compared with the pile driving operation itself. The investment for the drive unit must therefore bear a balanced, different relation to work above water.
Further, the expensive underwater equipment components are, in fact, utilized only rarely and then only for short time periods and should offer more diverse use, so that they can be amortized more quickly. Therefore, in view of the increasing need for economy in this established underwater technology, the current state of the art is no longer adequate.
DE-PS 30 07 103 discloses a drive unit which is located on or next to the housing of an impact hammer.
This drive unit consists of an electric or hydraulic motor and a pump. It does not have a pressure medium tank, but is connected with the fluid filled housing of the impact hammer. The fluid in this housing is simultaneously used as the drive fluid for the ram hammer and is pressurized by the pump. The pump and motor form a part of the hammer unit which is rigidly attached to the hammer housing. Advantageously, the pump with motor including all conduits is installed in the head of the hammer housing. An arrangement next to the hammer housing is not further explained. This drive unit, unlike previously described units, is not designed as a self contained drivable unit because it lacks a pressure medium tank, unless the surrounding water is used as the drive fluid which can restrict its operation depending on the degree of water fouling.
In addition, this design demonstrates some of the previously described disadvantages, i.e. the fixed connection of drive unit and supply line can only be disconnected onboard, access to the pressure medium cylinder etc. is obstructed and, because the connection is fixed and rigid, the handling risks to the supply lines described above and to the unprotected motor/pump unit apply.
The state of the art outlined above describes problems and/or wishes dealing with the drive unit itself and with other components or circumstances all of which inhibit, already for some time and increasingly so, the economic use of underwater drive units for the energy efficient operation of pile drivers and work units.